<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>

  <body>
    <div id="app">
      <h2>当前计数： {{counter}}</h2>
      <!-- <button v-on:click="counter++">+</button> -->
      <!-- <button v-on:click="counter--">-</button> -->
      <!-- 语法糖 -->
      <button v-on:click="add">+</button>
      <button @click="sub">-</button>
    </div>

    <script src="../js/vue.js"></script>
    <script>
      const app = new Vue({
        el: "#app",
        data: {
          counter: 0,
        },
        methods: {
          add: function () {
            console.log("add会执行");
            // 不能直接引用counter，才能引用app当中的counter  代理
            this.counter++;
          },
          sub: function () {
            console.log("sub会执行");
            this.counter--;
          },
        },
      });

      // 1 拿button元素

      // 2 添加监听事件
    </script>
  </body>
</html>
